Safety electrical outlet



Nov. 28, 1950 H. HUBBELL 2,531,625

SAFETY ELECTRICAL OUTLET Filed April 8, 1948 l NVENTO R f/araqy bGIJP/I BY RN EYS Patented Nov. 28, 1950 2,531,625 SAFETY ELECTRICAL OUTLET Harvey Hubbell, Long Hill, Conn., assignor to Harvey Hubbell, Inc., Bridgeport, Conn., a corporation of Connecticut Application April 8, 1948, Serial No. 19,682

7 Claims. (Cl. 200-51.09)

My invention relates to improvements in safety or shockproof electrical plug receptacles of the type used for wall outlets in buildings for plugging in electrical fixtures.

Electrical plug receptacles of the type under consideration are particularly adapted to overcome and avoid the potential sources of danger present in conventional type receptacles having slots or openings provided with live contact elements. The danger from such conventional receptacles results from the insertion, particularly by children, of foreign metal objects such as nails, pins or other metal objects into one or both of the openings, resulting in severe burns or electrical shock.

The primary object of the present invention is therefore to provide an improved safety receptacle structure, which will have application for use with various types of plugs and which is so constructed that the number of different parts to be manufactured are held to a minimum.

In general, my invention is an improvement upon safety electrical plug receptacles of the kind having a pair of openings to receive the prongs of an electric plug, an electrical contact located in the lower portion of each opening for engagement by a plug prong, a movable member for each opening located partly therein above the eectrical contact and in a position to be engaged and moved by 9. prong of the plug, and electrical connections actuated by the movement of the movable member associated with either of the openings, when a prong of the plug enters that opening, to close a path for electric current to the electrical contact located in the other opening of the pair. In such a receptacle the electrical contacts in both of the openings are normally dead and either of them can only be made alive by the movement of the movable member associated with the other opening, as by inserting a plug prong therein, to close the electrical connections actuated thereby. When the prongs of a plug are inserted in the openings of this receptacle, the electrical connections to the contacts are made up before the prongs engage the contacts and form a circuit, and when the prongs are withdrawn the circuit is broken at the contacts before the. electrical connections are disturbed, thereby avoiding arcing and welding in the electrical connections.

I have observed with respect to the prongs or blades 01' conventional type receptacle plugs, that while there is considerable variation in the width of the blades, most of them are made from metal stock 91 subst n y he same thickness.

One feature of my invention is therefore to provide a safety receptacle of the type described in which the movable members associated with the receptacle openings are arranged with respect thereto so that the thickness of the plug blades as they are inserted in the openings will be utilized for obtaining the necessarymovement of such members, for in turn actuating electrical connections to close a path forelectrical current from current supply conductors or terminals to contact elements located in theopenings. When the thickness of the plug blades, that is, their flat sides, are used, according to the invention, to move the movable members, therscope of usefulness of the receptacle is greatly increased since it may be made in various forms adapted for common use, including polarizedplug receptacles '3 and others especially constructed to receive plug blades of different widths.

In a preferred form of receptacle construction the movable members associated with the receptacle openings are made of insulating material in the shape of discs or rollers, one of which is provided for each outlet opening and located for free movement in a passageway opening through the side wall of the opening where it will be engaged by the fiat side surface of the plug prong. Relatively thin flat discs are advantageously used which normally project across the receptacle openings. The discs roll or rotate freely in their passageways and thereby increase the ease with which the plug prongs are inserted and withdrawn from the receptacle openings. This improved construction of the receptacle also includes a contact located in each opening and connected to a spring conductor arranged to I be moved by a disc or roller associated with a different opening into engagement with a current supply conductor or terminal located in the body of the receptacle. In an advantageous construction, the contact or contact element or member for each opening comprises a contact spring lo- -cated in or below the opening, and a spring conductorintegrally included in a single U'-shaped section of spring metal mounted edgewise in the body of the receptacle.

The-number of different parts necessary for making, a receptacle of this type is held at a minimum by making the contact members for all openings interchangeable and the samefor the 'curr'entsupply conductors and discs or rollers.

In making a receptacle according to the invention, the contacts located in, or associated with,

;the'.op'enings, and the rollers or discs associated therewith, are advantageously arrangedfwith respect to each other, so that when a prong of a plug is moved into an opening, it first engages the roller or disc to actuate the electrical connections or contact spring associated therewith, to close a path for electric current to the contact located in a difierent opening, and as the prong is further moved into the opening, it engages the contact therein so that there will be no welding of the contact spring, actuated by the disc, to its current supply terminal, although there may be the usual arcing when the plug prong engages the contact in the opening. The contact spring for each opening of the receptacle is advantageously located below or in the lower portion of the opening below the position or" the disc associated therewith so that when the blades of a plug are withdrawn from the receptacle, the circuit through the receptacle and plug will be broken at the contact springs. In this construction it will be understood that the actuation of s the electrical connections by one prong and the disc associated therewith, will only eifect the closing of a path for electrical current to the contact in a different opening.

In this application I illustrate and describe in detail one structural form embodying the features of the invention, it being understood that other structural forms may be made.

The detailed features of my invention are described hereinafter in connection with an illustrative embodiment thereof, shown in the accom panying drawings forming part of this application.

In the drawings:

Figure 1 is a vertical View partly in section taken on an irregular line approximating the line Il of Figure 2, showing the operative parts of a twin-type plug receptacle constructed in accordance with the features of my invention In this view the front portion of the body is removed and the surfaces of some of the parts in front of the line l-! are shown.

Figure 2 is a vertical sectional view taken on the line 2-2 of Figure 1 with the surfaces of some of the parts off this line being shown.

Fi re 3 is a broken sectional view taken on the line 3-3 of Figure 1.

Figure 4 is a broken perspective view showing parts of the mechanism in the left side of Figure 1 when removed from the body of the receptacle.

Figure 5 is an elevational side view of the twin receptacle shown in Figures 1 and 2,

Referring to the drawings, the improved receptacle comprises a body of insulating material consisting of a front section I6 and a back section 12 held together by screws or other locking means, not shown, so as to provide a substantially unitary structure having an external shape similar to conventional or other types of receptacles, The receptacle is provided with securingflanges 16 of conventional form suitable for mounting the receptacle in an outlet box. The flanges l6 carry removable washers !8 such as those provided with certain known makes of receptacles. The body of the receptacle also includes the usual projecting bosses 20 and 28a for each plug which areadapted to project through a conventional type cover plate, not shown.

The boss 20 is provided with rectangular shaped. slots 2 I and 2 la and the boss 28a is provided with similar slots, one of which is shown in Figure 3 at-22, these slots being adapted to receive the blades of electrical plugs. The twin, unit as shown in Figure 1 is illustrated in connection with ing yokes 36.

a plug 24 (Figure 2) with its blades 25 and 23a inserted respectively in the slots 2| and H12.

A pair of current supply wires 28 and 28a are connected respectively to similarly shaped current supply bars 30 and 32 fitted in recesses in the body and adapted to supply current to the two receptacles shown. The wires 23 and 28a are are clamped respectively to the bars 3 and 32 by means of screws 34 threaded in movable clamp- The current supply bar 35 is bent in the shape shown to provide contact terminals 30a and 301) which are of a width so that they are mounted in suitable openings or compartments in the body section [2. Th bar 32 is similarly shaped and mounted and includes contact terminals 32a and 32b.

The metal elements which are adapted to engage the current supply terminals and in turn supply current to contact springs beneath all of the slots of the receptacle are of the same structure, and the greater portion of each element or conductor is mounted in appropriate channels or cavities in the body section l2. As an example of the structure and arrangement of these conductors, reference is specifically made to the conductor for the slot 2| which comprises a substantially U shaped-metal element including a return-bend contact spring 38 provided with flaring top p'ortions'adapted to direct and'receive the plug blade 25'. This contact spring is mounted in a well in the body section 12 back of the slot 2! and is adapted to grip the blade 26 as it is inserted into the receptacle. The contact spring 38 is con nected to a' straight'section of metal which extends along the blade 26 to the bottom of the U 38a which is connected to the opposite leg of the U mount d in a cavity in the'section i2 and provided with a spring return-bend at its end forming a contact 381) arranged to engage current supply terminal 32b.

This conductor is provided with a forwardlyextending arm 38c adjacent to the contact 38?) which extends substantial y into the body section ll] as shown in Figure 2. The entire conductor including the foregoing elements are advantageously made of spring metal and arranged in the body of the receptacle so that after the contact 38b is moved into engagement with terminal 32b, current is supplied to the contact spring 38 and to the plug blade 26. The spring conductor for the blade 26a which is inserted in the slot 2|a includes a contact spring 40, a section 48a forming the bottom of the U, a contact 40?) and a forwardly-projecting arm Mic.

The plug receptacle at the opposite end of the unit includes a contact spring 42 for the slot 22, a portion 42a forming the bottom of the U, a contact 4212 adapted to engage terminal 32a, and a forwardly-projecting arm 42c. The conductor for the slot opposite 22 includes a contact spring 44, a portion 44 a forming the bottom of the U, a contact 44b adapted to engage the terminal 30b and a forwardly projecting arm 440. The con tacts 38b, 49b, 42b and 441) are normally sprung outwardly, as indicated by the position of the latter two contacts, while, the application of pressure to the arms 38c, 40c, 42c and 440 causes the respective contacts to spring toward the respective legs of the U shaped conductor, as shown by the contacts engaging the terminals 3Qq and 32b. The spring contacts such as 38, are mounted in wells in the body section [2 directly in back of the respective slots in the body section it).

Th ody. se ti n .12 is provid d w t v cav t es for receiving the U shaped conductors as shown.

the walls of such cavities being provided with projections adapted to hold the conductors in their correct positions. Thisarrangement may be described in connection with the conductor having the contact spring 38 which is bent around a cylinder shaped buttress 46 on the inside corner, which is offset with respect to a smaller cooperatin projection 48 arranged to hold the contact spring 38 properly aligned with respect to the slot 2|. At the opposite corner the U shaped conductor bears against a small buttress 50 on the inside of the U, and in the middle of the U it engages an outer buttress 52. These buttresses serve to hold the body of the conductor in position while permitting a certain latitude with respect to the ends of the legs of the U. It will be noted that with the plug removed, the legs carrying the contacts 42b and 44b, for example, are biased, so that they extend directly along the cavity wall opposite and spaced from the respective terminals 32a and b.

Each of the receptacle slots is provided in the section In with a lateral cavity or passageway. For example, in Figure 2, the slot 2| is provided with a passageway 54 and the slot Zla with a passageway Me, which open respectively from the sides of the slots into the cavities into which the arms c and 380 respectively project. Each passageway, such as 54, has a rectangular shaped opening into the respective blade slot, such as 2|, and it is relatively narrow compared to the width of the slots or blades as shown. A disc of insulating material such as a hard fiber or plastic disc is mounted in each of the passageways, as for example, a disc 53 is mounted in the passageway 54 and a disc 56a is mounted in the passageway 54a, directly opposite the respective arms 40c and 380. The four discs shown in Figure 1 have the same dimensions.

The shape of the passageway containing the disc in the face of the slot is illustrated in Figure 3 of the drawings which shows the slot 22 provided in its side wall with an oblong passageway 58 containing a disc or roller 60 which is directly opposite the arm 440. A disc 60a, is engaged by the arm 420 as shown in Figures 1 and 4.

The discs or rollers, such as 56, are mounted in their respective passageways, so that they are free to move and roll therein, and each is held in the osition indicated in Figures 2 and 3, completely within the body section I!) and substantially spaced from the main surface of the body section I2 by a projection 62 integralwith the body section l2. Each of these projections 62 have a plane forward surface forming one wall of the passageway in which the disc or roller is retained. I

The discs or rollers are of such a diameter that when disc 56, for example, is moved to the left in Figure 2 by the arm 40c, it will extend across the slot 21 to approximately the opposite wall and still be in engagement with the arm 400 when the contact 441) is in the position shown in Figure 1. The arms which are moved by the discs are sufficiently rigid with the legs of the U shaped conductors to press the contacts against the respective terminals.

When the blades 26 and 26a are inserted in the slots 2| and 2m, as shown in Figure 2, the flat outside surfaces of the blades respectively engage the discs and 56a, and push them outwardly against the arms 40c and 380 respectively, to move the contacts 40?) and 38b respectively into engagement with the terminals 30a and 32b, so that the current will be supplied to the contact springs 38 and 40. These movements are accomplished before the plug blades reach the respective contact springs, so that there is no arcing between the contacts 38?) and 40b and their respective terminals. As the blades 26 and 26a reach the contact springs 38 and 40, there may be arcing, but this is the same as that which occurs in conventional receptacles.

From a consideration of Figure 1 of the drawing, it will be noted that the return bend in the U shaped conductor forming the contact spring extends only over a portion of the plug blade and is offset with respect to the disc associated therewith. This arrangement permits the lips of the contact spring, as for example 42 in Figure 3, to extend into the body section l0 and there function in an adequate cavity at the side of the adjacent projection 62, which retains the disc in place. However, it is not necessary that the lips of the contact springs extend into the section I0, but the arrangement may be such that the contact springs are directly in back of the discs, such as when relatively narrow plug blades are used. The construction shown, however, provides an advantageous arrangement since the projection 62 can be more conveniently provided for with the contact springs and discs 011- set.

Figure 4 of the drawings shows the left-hand pair of U shaped metal conductor elements removed from the receptacle body and arranged in their relative positions with respect to each other and to the discs or rollers associated there-.

with.

The plug receptacle of the present invention provides a shockproof device which can be used in place of conventional types of receptacles. The structural features may be employed in the making of shockproof plug receptacles regardless of the position of one plug blade with respect to the other or the number of plug blades utilized. In any case, the arrangement is such that the contact spring for any one blade is made alive or connected to a current supply terminal only by the action of another blade. Furthermore, if a child should insert an object such as a nail or bobby pin into one of the slots of the plug, he might be able to actuate the roller or disc,

" normally projecting thereinto, sufficiently to close a circuit, but that circuit will only be to the opposite slot. It will be understood, however, that the insertion of relatively small objects into the slots will not be sufficient to move the roller and close a circuit. Furthermore, the roller or disc occupies only a portion of the width of the slot so that it would be relatively easy, as shown for example by the relationships in Figure 3, to insert a nail or bobby pin to one side of the disc 60 so that even if both prongs of the bobby pin were inserted in the respective slots of a receptacle, there would be no shock or short circuit.

-In the improved receptacle as described, it will be noted that the discs or rollers are mounted in the forward portion of the receptacle and that when engaged by a plug blade, the disc is free to roll as it is engaged by the blade, thereby providing a minimum of resistance to the insertion of the blades. The same is true when the blades are withdrawn from the receptacle, since the discs not only provide a sloping rounded surface but also a rotating member shaped so that it cannot possibly become wedged in its passageway. Its relative thinness compared with its diameter requires only a slot-like passageway which is substantially all closed off when the plugs are in the body associated with each slot, a movable contact member connected to the contact element for each slot and, extending alongside and spaced from a diiierent one of said plurality of slots, a current supply terminal arranged in said body on the side of each movable contact member opposite the slot alongside which it extends, a passageway in said body opening through a broad side wall of each slot, and a rotatable disc of insulating material movably retained in said passageway with its peripheral surface engaging the movable contact member extending alongside the adjacent slot, said disc being movable into and across the slot with which it is associated and adapted to be engaged on its peripheral surface by the broad side wall of a plug blade when inserted. in the slot and moved from the slot and to, in turn actuate the adjacent movable contact member into engagement with the oppositely mounted current supply terminal.

2. A receptacle as, defined by claim 1 in which the disc is mounted in a plane extending in the lengthwise direction of and at right angles to the broad side Wall of the slot with which it is associated.

3. An electrical plug receptacle comprising a body having a pair of slots oblong in crosssection extending thereinto for the reception of the blades of a plug, a contact element for each slot including a portion thereof arranged for engagement by a plug blade and a portion forming a spring contact member extending along a broad side of the other slot, a movable and rotatable disc of insulating material operatively arranged in said body between each spring contact member and the adjacent one of said slots, each spring contact member being adapted to urge the adjacent disc through an opening in a broad side wall of the adjacent slot, and a fixed terminal connector arranged adjacent each of said contact members normally out of contact therewith and adapted to be connected to a source of electrical energy, each of said discs being arranged to be actuated by a, plug blade inserted in the adjacent slot whereby the adjacent spring contact member is moved into engagement with the adjacent contact terminal to thereby close a circuit to the contact element for the other slot.

4. A receptacle as defined by claim 3 in which each disc is mounted in a plane extending in the lengthwise direction of and at right angles to the slot wall through which it is adapted to project, whereby its periphery is engagable by a plug blade in a manner adapted to move the disc.

5. A receptacle as defined by claim 3 in which the contact element for each slot is a U shaped fiat metal member mounted edgewise in the inner portion of the body of the receptacle and having a, forwardly extending arm on the portion comprising the spring contact member, said arm engaging the periphery of the disc associated with the adjacent slot.

6. In an electrical receptacle having a pair of openings to receive the blades of a plug, an electrical contact and a movable disc of nonconducting material located in each of the openings in position to be engaged by a blade, and

electrical connections actuated by the movable disc associated with either opening when a blade enters that opening to close a path for electric current from a current supply conductor to the contact located in the other opening, the improvement which consists in so locating the movable discs in the openings of the receptacle that the peripheral surface of each will be engaged by a fiat side surface of a plug blade.

7. An electrical plug receptacle comprising a body having a plurality of openings extending thereinto for receiving the prongs of an electrical plug, an electrical contact associated with each opening adapted to be engaged by a prong, a terminal connector for each contact adapted to be connected to a source of electricity but normally disconnected from its contact, said body having a laterally extending cavity opening into a side of each opening, a freely rotatable roller of insulating material mounted in each cavity with its axis at right angles to that of the opening associated therewith, a portion of said roller normally projecting across the opening with which it is associated, and, upon the insertion of a plug prong into the opening, being movable laterally in said cavity a distance approximating the thickness of the prong thereby connecting the contact associated with a different one of the plurality of openings, and only the contact associated with said different opening, with its terminal connector, the peripheral surface of said roller being adapted to roll on the side of the plug prong during the insertion of the latter into the opening.

HARVEY HUBBELL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,221,345 Davis Nov. 12, 1940 FOREIGN PATENTS Number Country Date 374,145 Italy Aug. 16, 1939 

